Field of the Invention
The present invention relates to a technique of supporting an operation to a three-dimensional virtual object arranged in a virtual space.
Description of the Related Art
Conventionally, three-dimensional CAD systems are used in the field of manufacturing and design, and can design a component and its cross section while three-dimensionally displaying them. For example, there is known a technique of, when observing a cross section, setting the position and direction of a cross-sectional plane serving as a reference (to be referred to as a cross-sectional operation hereinafter), changing the position of the cross section of a component by an operation on a CAD screen, and observing the cross section.
A virtual reality (VR) system has also been studied, in which design is performed by using a three-dimensional CAD system in a virtual reality space by using a head-mounted display (HMD) (Japanese Patent Laid-Open No. 2012-53631). Further, there is proposed the use of a mixed reality (MR) system in which a physical space and a virtual space are combined by using an HMD (Japanese Patent Laid-Open No. 2010-66898). An operation device that is operated by gripping it with the hand or the like, like a game controller, instead of a mouse or a keyboard, is also used in an environment where an observer wears an HMD and observes a virtual object while walking around a physical space.
However, in the cross-sectional operation during display in VR or MR, a cross section is operated with predetermined buttons of a game controller. When the line-of-sight direction of an observer differs from a predetermined direction, the operation direction of the cross section becomes opposite to the direction in which the observer views the cross section, and the observer may not operate the cross section intuitively.
For example, a case in which a cross section is operated in a coordinate system defined by the origin and three axes (X-, Y-, and Z-axes) of a coordinate system defining a space will be considered. Assume that the game controller is configured so that its up button is associated with a movement in the +Y direction, its down button is associated with a movement in the −Y direction, and a cross-sectional plane parallel to the X-Z plane is operated in the Y-axis direction. In this case, when the observer stands on the X-Y plane and turns his eyes in the +Y direction, the cross-sectional plane moves deep (i.e. away from the observer) with the up button indicating the +Y direction and forward (i.e. toward the observer) with the down button indicating the −Y direction. In this case, the operation direction of the observer and the movement direction coincide with each other, so the observer can perform an operation naturally. To the contrary, when the observer turns his eyes in the −Y direction (e.g. he turns around by 180°), the cross-sectional plane moves toward the observer with the up button indicating the +Y direction and deeper (away from the observer) with the down button indicating the −Y direction. That is, the movement direction becomes opposite to the operation direction of the observer. This is unnatural to the observer, and he cannot operate the cross section intuitively. In some cases, when the cross-section normal direction is not toward the observer (i.e. in the plane normal to the direction of the line between the observer and the cross section), he cannot confirm the cross section.